Vectorscope



K. SCHLESINGER 2,751,429

vEcToRscoPE 3 Sheets-Sheetl June 19, 1956 Filed June 5, 1954 June 19,1956 K. SCHH-:SINGER VECTORSCOPE 3 Sheets-Sheet 2 Filed June 3, 1954INVENToR .Ku/ Sc/i/@s/hger w SM June 19, 1956 K. SCHLESINGER 2,751,429

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United States Patent-'O VECTORSCOPE Kurt Schlesinger, Maywood, lll.,assigner to Motorola, Inc., Chicago, lll., a corporation of illinoisApplication June 3, 1954, Serial No. 434,144

13 Claims. (Cl. 178-5.4)

The present invention relates generally to apparatus for indicating theamplitude of a signal to be tested and the phase of such a signal withrespect to a reference signal, and more particularly to such apparatuswhich includes a cathode ray tube for displaying a representation of thesignal to be tested, preferably, as a vector indicating the amplitude ofthe signal and its phase displacement from the reference signal.

There are many instances in which it is desired to observe the relativephase of signals generated in various types of electronic equipment. Forexample, in color television systems of the type utilizing a colortelevision signal of present day standardized composition, it isdesirable to provide an indication of the phase relations of the variouscolor subcarrier components of the color television signal with respectto the color reference signal burst components thereof.

It is accordingly an object of the present invention to provide improvedapparatus for indicating visually the amplitude of a signal to be testedand the phase displacement of such a signal from a reference signal.

A further object of the invention is to provide such improved phase andamplitude measuring apparatus in which the phase of an unknown signalwith respect to a reference signal and the amplitude of the unknownsignal is shown as a vector or dot position with respect to a referenceaxis.

Yet another object of the invention is to provide such improved phaseand amplitude indicating apparatus in which the phase of an unknownsignal with respect to the reference signal and its amplitude isdirectly displayed on the screen of an oscilloscope by the use ofsignals derived from a combination of the unknown signal and thereference signal by relatively simple circuits contained within theapparatus.

Yet another object of the invention is to provide such improvedamplitude and phase measuring apparatus which may be adapted for use inconjunction with a color television signal of present-day standardized`composition andl which is constructed to respond to the colortelevision signal itself to provide an indication of the variouscomponents contained in the signal.

A still further object of the invention is to provide such improvedamplitude and phase measuring apparatus that may be adapted to provide avisual indication of the frequency deviation of a frequency modulationreceiver from the center frequency.

Yet another object of the invention is to provide such improved phaseand amplitude measuring apparatus that may be adapted to provide avisual indication of the characteristics of a passive network throughouta selected frequency band.

A feature lof the invention is the provision of a phase and amplitudemeasuring apparatus in which an unknown signal is compared with anin-phase component and with a phase-quadrature component of a referencesignal in a circuit containing a pair of discharge devices biased to aClass B condition for the reference signal to provide 2,751,429 PatentedJune 19, 1956 ice rst and second control signals, the first controlsignal having an amplitude corresponding to the amplitude of the unknownsignal and its phase displacement from the in-phase component of thereference signal and the second control signal having an amplitudecorresponding to the amplitude `of the unknown signal and its phasedispla-cement from the phase-quadrature component of the referencesignal.

Another feature of the invention is the provision of such improvedamplitude and phase measuring apparatus which incorporates an improvedphase-quadrature network for deriving the phase-quadrature component ofthe reference signal in such a manner that amplitude balance adjustmentsin the apparatus have no effect on the phase-quadrature characteristicsof the network.

Another feature of the invention is the provision of such improvedamplitude and phase measuring apparatus which may be directly connectedto a source of a presentday standard color television signal and whichincludes circuit means for recovering the color reference bursts fromthe color television signal and for using such bursts to produce areference signal of the frequency and phase of the bursts, and whichselects the chrominance subcarrier components of the -color televisionsignal for comparison with the derived reference signal to provide avisual indication of the respective amplitudes of the subcarriercomponents and the phase relation of each with respect to the referencebursts.

Yet another feature lof the invention is the provision of such improvedamplitude and phase measuring apparatus which includes circuit means forconverting frequency variations into phase variations so that theapparatus can be used to measure, for example, the modulation deviationof a frequency modulated transmitter from its center frequency.

The above and other features of the invention which are believed to benew are set forth with particularity in the appended claims. Theinvention itself, however, together with vfurther objects and advantagesthereof may best be understood by reference to the following descriptionwhen taken in conjunction with the accompanying drawing in which:

Fig. l is a schematic yrepresentation of the improved amplitude andphase measuring apparatus of the invention adapted for use inconjunction with a color television system utilizing a present-daystandard color television signal;

Fig. 2 is a wiring diagram of a phase detector portion of the apparatusof Fig. l;

Fig. 3 is a wiring diagram of the remainder 'of the apparatus of Fig. l;

Fig. 4 is a mechanical representation of a manually variable delay lineused in the circuit of Fig. 2;

Fig. 5 shows the display on the screen of the reproducing tube used inthe apparatus of Fig. l indicating various -chrominance sub-carriercomponents of standard color television' signal;

Fig. 6 shows a modification of the improved apparatus for use inmeasuring the frequency deviation of a frequency modulated signal fromthe center frequency;

Fig. 7 shows the display of such frequency deviation on the screen ofthe reproducing tube; and

Fig. 8 is another modilication of the improved apparatus of theinvention for use as a measuring means of the characteristics of apassive four-terminal network.

The invention provides apparatus for indicating the amplitude of asignal to be tested and the phase of such a signal with respect to areference signal of greater amplitude and of like frequency. Theapparatus comprises rst and second discharge devices with means forbiasing the devices to a Class B condition for the reference signals. Alirst input circuit is coupled to the dis- Vacross the screen in avertical direction.

charge devices for impressing thereon the signal to be tested; and asecond input circuit is coupled to the first discharge device forimpressing an in-phase component of the reference signal on the lirstdevice, and the second' input circuit includes a phase-quadraturenetwork for impressing a phase-quadrature'component of the referencesignal on the second device. A cathode-ray tube is provided which has aviewing screen, and which also hasl iirst-and second deflection meansfor deiiecting the cathode-ray beam therein across the screen inmutually perpendicular directions. A irst output circuit is coupled tothe Yiirst discharge device for deriving a first control signal havingan amplitude correspondingto the ampli- Ytude of the signal to be testedand also to the phase displacement of that signal from the in-phasecomponent of the reference signal. A second output circuit is coupled tothe seconddevic'e for deriving a second control signal having anamplitude corresponding to the amplitude of the signal to be tested andalso to the phase displacement of the signal from the phase-quadraturecomponent ofthe reference signal. Final-ly,- rn-eans is provided forirnpre'ssing the nrst and second control signals respectively on theiirst and second deflection means of the cathode-ray tube.

As previously stated, the apparatus of Fig. l isV constructed to beutilized in conjunction with a color television system of present-daystandardized composition; The apparatus includes a first probe whichwill be referred to herein as the test signa probe, and probe 10 iscoupled to a band pass ampliiier 11 through a variable resistor 12having one side connected to a point of reference potential or ground.Unit 11 is coupled tov a modulator amplitier 13, and a local oscillator14 is also coupled to this amplier. The output terminals of unit 13 arecoupled to a variable delay line 15 which, in turn, is coupled to aphase and amplitude detector 16 and to a phase and amplitude detector17.

The apparatus also includes a probe 18 which will be referred to hereinas the reference signal probe, and probe 18 isconnected to an amplilierand color synchroni'zirng burst separator 19 through a variablepresistor20, the resistor having one side connected to the point of referencepotential. Unit 19 is connected through a burst regenerator 21 to anamplitude limiter stage 22. The output terminals of limiter 22 areconnected to detector 16 and through a quadrature network 23 to detector17.

'A cathode-ray reproducing tube 24 is provided and this tube has a pairof deflection'electrodes 25 for deflecting the cathode ray beam thereinin a horizontal direction across the viewingV screen 10'7 and the tubealso has a pair of deflection electrodes 2,6 for deilectingthe beamThe'pout'put terminals of detector 16 are connected to thehorizontald'efiection electrodes 2S, and the output terminals of detectorV 17 areconnected to the vertical deflection electrodes 26. f

As is well-known, the present-day standardized color television signalincludes monochrome video-frequency components, synchronizingcomponents, color reference signal color bursts, and a chrominancesub-carrier amplitude modulated in Vphase quadrature by respectivechrominance signals.` BlockV30 represents a source of such a televisionsignal, and this source may be a color television receiver or monitor orany other apparatus in which'it is desired to determine the amplitude ofthe chrominancesub-carrier components and their phase displacement fromreference as the television signal appears at various points in theapparatus.

Probes 10, 18 are of the low capacity type. The arrangement is such thatprobe 18 can be connectedl to a point where the color television signalappears, and itschannel automatically derives a reference signal fromthe color televisionsignal. When so desired, however, probe 18 can beconnected to any reference signal source of appropriate frequency. Probe10, onV the other hand, can be connected to any point in source 30wherein it is desired to measure the amplitude of the chrominancesub-carrier components and their phase relations with the color signalbursts, and its channel is capable of selecting these components fromthe color television signal. Y Probe 18, however, can. be connected toany point where a signal appears Whose amplitude and phase relation witha reference signal is of interest.

The color television signal as picked up by probe 10 is ampliiied inampliiier 11.` As previously noted, the amplifier is of the bandpasstype, and it is selective only to the frequency range ofthe chrominancesub-carrier components (for example, from 2.5-4.7 megacycles), and itrejects interference such as motorboating, microphonics and hum. Theamplified chrominance sub-carrier cornponents are supplied to detectors16 and 17 through units 13 and 15.

The color television signal picked up by probe 1S, on the other hand, isamplified by the amplifier inunit 19 which responds to the fullfrequency range of the color television signal. (For example, from 0 5megacycles). Unit 19 also includes circuitry for removing thesynchronizing components from the color television signal and for usingthese components to recover the color reference bursts from thetelevision signal. The recovered color reference bursts are impressed'on the burst regenerator 21 and cause it`to generate a continuous wavereference signal havingV the phase and frequency of the reference colorbursts. The reference signal from Vunit 21 is amplitude limited inlimiter 22 to a constant value at Yleast Vtwice the maximum amplitude ofthe chrominance sub-carrier components, and the amplitudelimitedreference signal impressed on detector 16 and through phase-quadraturenetwork 23 on detector 16.

Detector 16 responds to the chrominance sub-carrier components and tothe in-phas'e component of the reference signal from limiter 22 ytoproduce for each of the subcarrier components a unidirectional controlsignal having an amplitude corresponding to the amplitude of thecorresponding sub-carrier componentand also corresponding to its phasedisplacement from the in-phase component of the reference signal.Detector 17, on the other hand, responds to the sub-carrier Componentsand to a phase-quadrature component of thereference signal toproduce-for each of the sub-carrier components a unidirectional controlpotential having an amplitude corresponding to the amplitude'of thecorresponding sub-carrier component and also corresponding to its phasedispiacement from` the phase-quadrature component of the referencelsignali The unidirectional control signal from detector 16 is applied todefiection electrodes 25", and it deiiects the cathode-ray beaminrreproducin'g device 24 along the horizontal aXis inV a direction andby'an amount corresponding'to the amplitude of each ofthe sub-carriercornponents and also corresponding to the respective phase displacementthereof from the'Vin-phase component of the reference signal. Thecontrol potential from detector 17 is` applied to the verticalelectrodes 26 to denect the cathode-ray beam along a vertical axis in adirection and by an amount corresponding to the amplitude of therespective sub-carrier components and -also corresponding to theirrespective phase displacements from'V the phase-quadrature Vcomponentofthe reference signal. The resulting indication on they screen ofdevice 24 is a series of uorescent dots displacedV from the center ofthe screen by amounts corresponding respectively to the amplitudesof thesub-carrier components and having angular positions 'corresponding'respectively to the phase displacements of the sub-carrierV componentsfrom the reference signal.

It is convenient that the indicationY be. represented by vectorsrather'than dots, andfor thatxreason; theV local oscillator 14 isprovided which generates a signal, preferably a sawtooth wave (of,forlexample, -10 kilocycles), which periodically reduces the gain ofamplier 13 to zero to produce an amplitude modulation on the subcarriercomponents. This simple expedient causes the dots referred to previouslyherein to be periodically swept to zero so that the respectiveindications are by vectors rather than dots.

Any one of the vectors or dots referred to above can be aligned with areference axis on the screen of device 24 by manually adjusting variabledelay line 15. Such manual adjustment imparts a uniform delay to each ofthe sub-carrier components which causes their indications to rotate onthe screen of the reproducing device.

Fig. 5 shows a typical indication on the screen of the reproducingdevice 24 of the usual sub-carrier components in a standard colortelevision signal. This particular indication corresponds to thetransmission of vertical color bars. The colors transmitted were red,yellow, green and blue. The angles and radials of the display arecompared for test purposes with the standard values tabulated below:

A circuit diagram for units 13-17 and 23 is shown in Fig. 2, and asshown in that figure, modulator amplier 13 includes an electrondischarge device 40 connected in known manner to constitute an ampliiierstage. Local oscillator 14 includes an electron discharge device 41connected in known manner as a blocking oscillator to constitute asawtooth generator. The anode of device 41 is coupled to the screenelectrode of device 40 to impress the sawtooth wave on the screenelectrode of the latter device. This causes the gain of the amplifierperiodically to be reduced to zero, and the subcarrier componentstranslated thereby to be 100% amplitude modulated by the sawtoothsignal.

The anode of device 40 is coupled to the input terminal of variabledelay line through a triple tuned coupling network L11a-41e of knownconstruction and exhibiting relatively wide band pass characteristics.Network lila-41e passes the band of a chrominance sub-carrier componentsextending, for example, from 2.5-4.7 megacycles, and supplies thesecomponents to the delay line 15. The band-pass network 11a- 41e isdamped by the resistors 42, 43 in the anode circuit of device 40 whichassist in providing a uniform response characteristic for the networkover the band-pass range. Delay line 15 includes an inductance coil 46having an input terminal connected to the junction of coils 41C and 41e,this terminal being coupled to ground through a capacitor 45. Coil 46has an output terminal connected to ground through an inductance coil 47and series resistor 48. Elements 47, 4S serve to terminate the delayline in its characteristic impedance to prevent standing waves in theline. This termination also provides a resistive input impedance for thedelay line which further damps network 4in-41e and assists in providinguniform bandpass characteristics over its band-pass range.

The variable delay line 15 has a moveable coil 49 whose sides areconnected respectively to the inner and outer lines of a coaxialconductor 50. The inner line of conductor 50 is connected to the controlelectrode of an electron discharge device 51. Device 51 is connected asan amplifier and is cascade coupled to a second amplier includingdischarge device 52. The anode of device 52 is coupled to ground througha capacitor 53 and a series-connected inductance coil 54, and thejuncytion of elements 53, 54 is coupled through a capacitor 55 Vto thelcontrol electrode of an electron discharge device 56.

The mechanical details ofthe variable delay line 15 are shown in Fig. 4,and this delay line comprises a single layer helix coil 46that is woundaround a grounded metal tube 57 composed, for example, of brass andhaving a longitudinal slot 58 extending along its length. The tube, forexample, may be 9 long with an inside diameter of 1/2 and an outsidediameter of 1%6", and with a Ms wide slot. These dimensions areappropriate for a 3.6 megacycle chrominance sub-carrier as is presentlyused, and establish a full Wavelength of such sub-carrier along theline. The moving pickup coil 49 is closely wound in an annular slotaround the periphery of a moveable member 59 composed, for example, ofbakelite or other insulating material and having an outside diameter,for example, of l. The width of the peripheral slot may, for example, be1A" and its depth l/le. The inner member 59 is manually slidable withintube 57 to provide a complete 360 time delay of the signals translatedby the unit.

Device 56 is connected to form, in conjunction with a device 65, thedetector 16 of Fig. l. These devices preferably are beam tetrodes andare connected in push pull to have an overall gain, for example, of :1.This detector is in the form of a pulsed envelope detector of a typesimilar to those disclosed and claimed in copending application SerialNo. 372,697 iiled August 6, 1953, in the name of the present inventor.As fully discussed in that application, a pulsed envelope detector ispredicated on the principle that half wave rectification of a compositesignal formed by an amplitude modulated test signal and reference signalof the same frequency and at least double the amplitude produces anoutput signal corresponding to the amplitude modulation of the testsignal and to the phase displacement of the test signal from thereference signal.

To perform the function described above, devices 56 and 65 are biased tofunction as Class B amplifiers for the reference signal impressedthereon, and this bias is obtained by returning the respective controlelectrodes of these devices through a grid leak resistor 66 to thenegative terminal of a biasing source C-. source may be a battery or anyother convenient source of negative unidirectional potential of theappropriate value to bias the devices to Class B operation for thereference signal.

The cathodes of devices 65 are connected together through a phaseinverting inductance coil 67, preferably of bi-filar construction, whosemidpoint is connected to the point of reference potential or ground. Theanodes of the devices 56 and 65 are connected to the positive terminalB-I--lthrough respective band-rejection filters 68a-68d, 69a-69d; andthrough respective low-pass lters 68e-68k, 69e-69k. These lilters rejectthe subcarrier and its sidebands and pass only the detected componentsfrom 0-11 kilocycles. The connection to the positive terminal B-I--I- ismade through a variable potentiometer 70 whose moveable tap can beadjusted to control the horizontal centering on reproducer 24.

The screen electrodes of devices 56, 65 are connected to the positiveterminal B-lthrough a screen dropping resistor 44a and are coupled toground through respective bypassing capacitors 44b, 44e. A neon tube 44dis also coupled between these screen electrodes and ground to assureconstant potential on the screens in the presence of control signalvariations of the control electrodes.

The cathode of device 56 is coupled to the cathode of an electrondischarge device 71 through a variable capacitor 72, and the junction ofthe capacitor and the cathode of device 71 is connected to the point ofreference potential through a variable resistor 73. The output circuitof the amplifier of discharge device 52 is coupled to the controlelectrode of device 71 through a capacitor 74, and this output circuitis connected to ground through a pair of series resistors 75, 76,resistors 75 being variable This biasing 7 for Vgrain balancepurposes tocompensate for deflection irregularities in reproducing tube `24. Y Y

Device '71 anda further ydevice 92,`like devices 56 and 65, areconnected as Class B amplifiers for the reference signal Ycomponentapplied thereto. To achieve this, the control electrodes of Vthesedevices are also connected to the negativeV biasing terminal C through aVtive'low-pass 'filter and band rejection networks 79, 80 which performthe'same function as networks 685;-68/c,

69-.69k; and the kanodes are connected to the positive terminal throughaV variable potentiometer Si which provides vertical centering forreproducer 24. The screen electrodesof devices 71, 92 are connected tothe screen electrodes of Vdevices 56, 65.

The .circuits of devices 56, 65 are connected respectively to thehorizontal deflection electrodes of device 24 andrprovidre adirect-current path thereto; and the circuits 79, `80 of devices 71, 92are connected respectively toV the vertical deflection electrodes 26 ofthe reproducer and provide a direct-current path thereto. Thearrangement of Fig. 2 has an input terminal Q that is coupled through ablocking capacitor 81 to the cathode of device 56.

in the circuit of Fig. 2, itis assumed that one or more signals to betested are impressed across input terminal P and ground; that a likefrequency double amplitude reference signal is impressed between theterminal Q and ground. The signal to be tested is impressed with likephase on the control electrodes of devices 56, 65, 71 and 92. Thereference signal, on the other hand, is impressed on the cathode ofdevice 56 with its original phase, but is impressed on the cathode ofdevice 65 with inverted phase for push-pull operation of devices 56, 65,the phase inversion being achieved by inductance coil 67. As previouslynoted, thedevices are biased to function as Class B amplifiers forreference signal components impressed thereon and produce in theirrespective output circuits a signal corresponding to the amplitude ofthe test signal and to the phase displacement thereof from the referencesignal. Due to the push-pull operation of the devices, the controlsignal produced in their output circuits are of opposite polarity whichis desired so that these output control signals may be applied to thedeflection electrodes 25 of device 24. Y

Capacitor 72 (c) in conjunction with the equal inductance portions (L)of inductance coils 67 and 78 connected between that capacitor and thepoint of reference potential, and variable resistor 75 (r2) form a lowimpedance quadrature network of a tuned lt type, and the quadraturephase between the output and input of this network is unaffected byvariations in the load balance resistor 75, just as long as one `Lcbranch is tuned to resonance. The basic relations of the tuned A aredescribed by the equations: ez=e1jr2/Z (where e2 is output signal, er isinput signal, and Z=\/L/c), and w2Lc=l. The input limpedance is a pureresistance r1=Z2/r2. Therefore, the amplitude balance between thereference signal and its phase quadrature component can be adjusted byvarying resistor 75, but the input impedance stays resistive and thephase-quadrature relation is not changed.

The phase quadrature component of thereference signal from thequadrature network described above is supplied to the cathode of device71, and this component is phase inverted by inductance coil 78 andapplied to the cathode of device 92.V The circuits Vof devices 71, 92,therefore, compare the signal to be tested with the phase quadraturecomponent of the reference signal; these de- 'i8 vices produceinntheirroutputk circuits a pair of push-pull control signalsrespectivelycorresponding to the amplitude of the test signal and thephase displacement `thereof from the reference signal.

Thecathode ray beamin device 24, therefore, is deflected along its Xaxis by an amount corresponding to the amplitude of the test signal andits phase displacement from the in-phase component of the referencesignal. Moreover, the deflection of the cathode ray beam along its Yaxis corresponds to the amplitude of the test signal and its phasedisplacement from the phase quadrature component of the referencesignal. The beam, therefore, is established at a position representingthe amplitude and phase ,displacement of the test signal from thereference signal. As previously noted, the periodic reduction if theamplitude of the test signal to zero produces a vector representation ofthe test signal rather than a dot representation.

Expressed mathematically: Y

The signal input to devices 56, 65 and 71, 92Y may be expressed as:

e=A cos (wt-Hp) (l) where:

A is the amplitude of the test signal o is the phase displacement of thetest signal fromrtheV reference signal.

The reference signal input may be expressed as:

eT=2 cos wt The amplitude factor 2 is chosen to indicate the use Thecircuit of devices 71, 92 operates on the signal (l) and on the phasequadrature component of the signal (72)., that is:

The filtered low frequency output of the circuit of devices 71,'92 thenbecomes:

-The detected control potentials ex and ey result in a stationary dot onthe screen of reproducer 24 with the desired polar co-ordinates A (t)(t). As previously noted, it is frequently desirable to enhancevisibility of the display by providing radials from each dot to center.This eUzA sin qb may be'accomplished by periodically keying the signal iamplitude to zero ata specified rate. The keying process in the presentinstance is shown as accomplished in unit 13 (Fig. l) prior to detectionwhich is inherently simpler than Vpost detection methods.

The circuit of Fig. 2 may be considered to represent the basic circuitof the vectorscope, whereas the circuit of Fig. 3 represents the'additional circuitry necessary to adapt the vectorscope to a directindication of the'various components of a color television constitutedin accordance with present-day standards, and as described inconjunction with Fig. l.

As shown in Fig. 3, .the test signal probe 10 of Fig. l is coupledthrough variable potentiometer 12 and a capacitor 91 to the controlelectrode Vof an electron dischargedevice 93. Device .93 in conjunctionwith an electron discharge device 94 forms the amplifier 11 of Fig. l.This amplifier is of the feedback type and is connected in known manneras a band-pass amplifier. That is, vthe `amplifier formed by devices493, '94 .selects .only the'2;45

4.7 megacycle band occupied by the chrominance spectrum so that only thecolor sub-carrier components are selected and supplied to terminal P ofthe vectorscope.

The reference signal probe 18 of Fig. 1 is coupled through potentiometer20 to the input circuit of an electron discharge device 96, the inputcircuit including a series capacitor 97 and grid leak resistor 98, thelatter connecting the control electrode to the point of referencepotential or ground. Device 96 is connected in cascade with anadditional electron discharge device 99 as a feedback amplifier. Thisamplifier is of known construction, and is designed to select thecomplete Video spectrum of the color television signal from zero tomegacycles.

The anode of device 99 is coupled to the control electrode of anelectron discharge device 100. Device 100 functions as a phase splitterstage, and its circuit includes a switch 101 which in one positioncouples its cathode to the control electrode of an electron dischargedevice 102 and which in its other position couples the anode of device100 to the control electrode of device 102.

Device 102 is cathode coupled to a pair of electron discharge devices103, 104, the latter two devices functioning as a synchronizing signalseparator. The separator circuit of devices 103, 104 includes a cathodefeedback connection so that the circuit saturates at two denite signallevels for ecient separation of the synchronizing components from thecolor television signal.

The separator circuit of devices 103, 104 is connected through a delayline 105 to the control electrode of an electron discharge device 106.The anode of device 102 is also coupled to the control electrode ofdevice 106 through a coupling transformer 107 which is tuned to thecolor subcarrier frequency, the connection from the delay line to thecontrol electrode being made through the secondary winding of thetransformer.

Device 106 is connected as an amplifier circuit and its output circuitis connected through a switch 108 to a crystal burst regenerator circuitincluding an electron discharge device 109. This circuit is known, andit responds to the color reference bursts to produce a continuous wavesignal having the frequency and phase of these bursts. Device 109 isconnected to a discharge device 110 so that when switch 108 is movedfrom its L to its O position, an oscillator circuit is established whosefrequency is stabilized by crystal 111. The anode of device 109 iscoupled to the control electrode of an electron discharge device 112which functions as an amplitude limiter. The anode of device 112 isconnected to the positive terminal B-lthrough a variable inductance coil113 and a resistor 114. The junction of these elements is coupled to theterminal Q of the circuit of Fig. 2 through a coupling capacitor 115. Asshown in Fig. 2, input terminal 4 is connected to quadrature network 67,72, 78, and as previously pointed out, the input impedance of thisnetwork is resistive when it is tuned to the frequency of the referencesignal. For appropriate high power coupling between limiter 112 and thequadrature network, coil 113 is tuned to resonate with the platecapacitance 116 of device 112 at the reference signal frequency.

The operation of this channel of the receiver has been describedpreviously herein, but this operation will be reiterated briey and is asfollows. 'I'he demodulated color television signal is amplied by theamplifier circuit of devices 96, 99 and impressed on the phase splittercircuit of device 100. The phase splitter circuit is included so thatthe instrument may be used when the demodulated signal has apositive-going synchronizing polarity or a negative-going synchronizingpolarity. For either polarity, it.. is merely necessary to set switch101 in such a manner that the demodulated color television signal isimpressed on device 102 with its synchronizing components extending in apositive-going direction. The demodulated color television signalappears in the cathode circuit of device 102 and the synchronizingcomponents are selected therefrom in the circuit of devices 103, 104.The selected syn- `10 chronizing components are delayed in delay line sdthat they appear in time coincidence with the color reference bursts,and the delayed synchronizing pulses are used as gating pulses fordevice 106. The cathode of device 106 is returned to ground through arelatively high biasing resistor 117 to enable the device properly toprovide the gating function. The anode circuit of device 102 impressesthe demodulated color television signal on the control electrode ofdevice 106, and this control electrode is pulsed by the pulses generatedby delay line 105 so that device 106 translates only the color referencebursts.

The circuit of crystal 111 and discharge device 109 is usually termedthe burst regenerator, and when switch 108 is in its L position, thecolor reference bursts impressed on the crystal cause the circuit toproduce a reference signal having a frequency of, for example, 3.58megacycles corresponding to the frequency of the reference signal burstsand to the frequency of the subcarrier components, and having a phasecorresponding to the phase of the reference signal bursts.

The television signal is sufficiently amplified in channel describedabove so that the reference signal developed' by the burst regeneratorhas an amplitude exceeding twice the amplitude of each of the subcarriercomponents. This: reference signal is amplitude limited by device 112so'- that the reference signal impressed on terminal Y has a; constantamplitude that is at least double the amplitude:

of the sub-carrier components.

The circuit of Fig. 2 may also be adapted so that the instrument may beused to measure the frequency deviation of a frequency modulation signalfrom its center frequency. Such an adaptation is shown in Fig. 6. Thatfigure shows a source of frequency modulated signals such as a frequencymodulation monitor receiver including the usual radio frequencyamplifier 120, first detector 121, intermediate frequency amplifier andlimiter 122, second detector 123, audio amplier 124, and soundreproducer 125, all of these stages being cascade connected in knownmanner. A probe 126 is connected to the output of intermediate frequencyamplier and limiter 122 to derive the frequency-modulatedamplitude-limited signal. Probe 126 is coupled through a time delaynetwork 128 to a modulator 129. The probe is also connected through amodulator 130 and band-pass ilter 131 to the modulator 129. A referencesignal generator 132 is connected to the modulator 130; and modulator129 and generator 132 are respectively connected to the terminals P andQ of Fig. 2. It is to be noted that the burst regenerator 21 of Fig. 3can conveniently be used to function as the reference signal generator132, it being merely necessary to change the position of switch 10S tothe oscillator position O to derive a constant amplitude referencesignal at the instrument frequency. This signal may conveniently bederived from terminals 127 (Fig. 3) connected to an inductance coil 133which, in turn, is coupled to coil 113 in the anode circuit of limiterdevice 1,12.

The amplitude-limited frequency-modulated signal from probe 126 (foiAf)is heterodyned in modulator 130 with the reference signal (fr) fromgenerator 132. Modulator 130 develops the sum and difference frequenciesof the signals, and bandpass lter 131 selects the sum frequency (fo-Hr)iAf. The band-pass filter produces, therefore, a series offrequency-displaced heterodyned signal components resulting from theheterodyne action of the frequency-rnodulated signal (faihf) with thereference signal (fr) from generator 132.

The amplitude-limited frequency-modulated signal (foiAf) from probe 126is time delayed in delay network 128 which imparts a phase shift to eachof the sideband components thereof proportional to its deviation fromcenter frequency (fo). A ferrite core delay line made by the ColumbiaTechnical Corporation is especially suited for this purpose. The outputsignal (einem) 2,55 ifie The-circuit of Fig. 2 compares the referencesignal withY the output signal of modulator 129 to produce a display onkthe-screen of reproduced device 24 such as shown in Fig. 7. It ispreferable that the time delay network 123 be designed so thatthemaximum permissible frequencyl displacement produces 180 deviations onthe screen .of tube 24. By present day frequency modulation standards,the allowed deviations are plus or minus 75 kc. so that the requireddelay of network 1'28 equals l 4 6),- 3.3 microseconds The instrumentcan Valso beused to monitor the frequencymodulated intercarrier soundcomponent `of a televisionsignal. In the latter system, the alloweddeviation of the frequency modulated signal is 25 kilooycles so that therequired delay of line 128 is 10 microseconds.

Therefore, Awhenever the frequency-modulated signal exceeds thepermissible deviation, the display on the screen of .reproducing device24 immediately indicates this fact bythe segment of the traced signalexceeding 180. Moreover, the Vfan shaped path reaches ya spread of 180only for peak deviations. In addition, the fanned out area will be asegment ofa circle as long as the receiver limiter is operatingproperly, andany spurious amplitude modulation is readily detected as aknown circularity of the displayed boundary. As in the precedinginstance, the display may be in the form of a vector representation bythe modulation of amplifier 13 (Fig. 2); and the display-may beangularly positioned on the screen of tube 24 by manual Aadjustment ofdelay line 15 (Fig. 2).

The circuit .of Fig. 2 can also be adapted to measure tude Vin eachcycle. Generator 135 is coupled to a phase splitter circuit including anelectron discharge device 138. Device .138, in turn, is coupled to apair of discharge devices 139, 140. Devices '139, 140 are connected -tofrequency modulate the output signal of an oscillator including aydischarge device 141, this frequency modulation being in accordancewith the signal derived from generator 135. In this manner theoscillator of device 141 generates a signal having, for example, acenter frequency of 10.7 megacycles which is frequency modulated so thata total deviation of i one megacycle is accomplished in steps, each 200kc. apart', at a repetition rate of 60 cycles.

The circuit of devices 138, 139, 140, 141 is generally termed anelectronic wobbulator circuit, and the illustrated circuit may bereplaced by others of this type. For example, a klystron'wobbulatorcircuit can be used, and this type is capable of providing a relativelywide kfrequency deviation at a relatively large number of discretesteps. It is desirable that generator 135 produce Ystepped waves .thatincrease linearly to maximum amplitude, so as to avo'id spuriousindications on the Screen of tube 24.

TheV frequency-modulated output signal from oscillator 141 is suppliedto an amplitude limiter stage 142, and

the limiter is coupled through the network under vtest 143 Y to themodulator 129. e The limiter 142 yis also coupled through the modulator130 and band-passiilter -131Ytoithe modulator r129. The reference signalgenerator 132 is coupled to modulator 130 and tofterminal Q of the cir-12 cuit 'of Fig. 2, whereas modulator 129 is coupled to terminal l ofthe `circuit of Fig. 2.

The amplitude-limited frequency-modulated signal from limiter 142 isapplied to the network under test, so that the latter network developsan output .signal having a plurality of discrete frequency components,each of the components having a phase displacement and amplitudecorresponding to the phase-shift and attenuation character'istics of thenetwork at Vthat particular frequency.

The signal from limiter 142 is also heterodyned in modulator with thereference signal from generator 132, and as in the system of Fig. 6, thesum frequency heterodyne components are passed to modulator 129 byband-pass filter 131.Y Modulator 129 heterodynes the various componentsof the output signal from the network under test in each instance to thereference frequency. Therefore, reference signal generator Y13 2impresses the reference frequency signal on terminal Q, .and modulator.

129-impresses a series of discrete signals on terminal P each having thereference frequency, and each being displaced in phase by ,an amountcorresponding to thephase displacement characteristics of the networkunder test at the different frequencies. Moreover, each component ofVthe output signal from network 143 has an amplitude corresponding tothe `attentuation characteristics of the' network at the variousfrequencies. Therefore, the vectorscope indicates visually .the phasedisplacement characteristics of the vnetwork ,under test at variousdiscrete frequencies, and also indicates the attenuation of the net-VYwork at .each such frequency. In other words, if the network undertestis a bandpass lter, the passband vis recognized as that sectionofthe vector envelope which most nearly approaches -a circle through theoriginV at= maximum radius. Constant phase delay, on the other hand, isrecognized by equal angles between consecutive radials. Crowding orspreading of these angles signifies phase distortion at the respectivefrequencies.V

The invention provides, therefore, an improved appa-V ratus forindicating the phase displacement -of a signal under test from areference signal and also the amplitude of the test signal. As describedherein, the indication is direct and easily ascertained, and theinstrument can be adapted to have a wide variety of uses.

VWhile particular embodiments of the invention have' beeny shown anddescribed, modifications may be made and it is intended in the appendedclaims to .cover :all such modifications Vas fall within the true spiritvand scope of the invention.

I claim:

l.V Apparatus for indicating vectorially the `amplitude of a signal tobe'tested and the phase of such .a signal with respect Vto a referencesignal of like frequencywand .of Vat least double ythe amplitudethereof, said-apparatus including in combination, rstand Vseconddetector means each responsive to Va pair .-of input signals of likefrequency for producing an output signal of an amplitude correspondingto the amplitude of one of the input signals Aand to the phase relationbetween such input signals, a first input circuit for ,impressing thesignal .to .be :tested on said first and second detector'means, yfirstcircuit meansfor supplying thesignal to be tested to said iirst inputcircuit, a modulator 'included in .said first circuit means *forperiodically varying .the amplitude Yof the test signal, a second inputcircuit for impressing .an in-.phase component of the reference .signalon said iirst detector means and ray tubehaving ,aviewing screen and,furtherih'aving first and -second'deflection means for deilecting acathode-ray" beam in the tube across said viewing screen in mutuallypelpendicular directions, a rst output circuit coupled to said firstdetector means for deriving a rst control signal therefrom having anamplitude corresponding to the amplitude of the signal to be tested andto the phase displacement of such signal from the in-phase component ofthe reference signal, a second output circuit coupled to said seconddetector means for deriving a second control signal therefrom having anamplitude corresponding to the amplitude of the signal to be tested andto the phase displacement of such signal from the phase-quadraturecomponent of the reference signal, means for impressing said rst controlsignal on said irst deflection means of said cathode-ray tube, and meansfor impressing said second control signal on said second deflectionmeans of said cathode-ray tube.

2. Apparatus for indicating the individual amplitudes of a series oflike-frequency phase-displaced signals to be tested and the phase ofeach of such signals with respect to a reference signal oflike-frequency and of at least double the amplitude of each such signal,said apparatus including in combination, iirst and second detector meanseach responsive to a pair of input signals of like frequency forproducing an output signal of an amplitude corresponding to theamplitude of one of the input signals and to the phase relation betweensuch input signals, a first input circuit for impressing the signals tobe tested on said first and second detector means, first circuit meansfor supplying the signals to be tested to said rst input circuit andincluding manually operated variable time-delay means, a second inputcircuit for impressing an in-phase component of the reference signal onsaid first` detector means, and including a phase-quadrature network forimpressing a phase-quadrature component of the reference signal on saidsecond detector means, second circuit means for supplying the referencesignal to said second input circuit and including amplitude limitermeans for establishing the reference signal at a constant amplitude ofat least double the amplitude of the signals to be tested, a cathoderaytube having a viewing screen and further having first and seconddeflection means for deiiecting a cathode-ray beam in the tube acrosssaid viewing screen in mutually perpendicular directions, a rst outputcircuit coupled to said rst detector means for deriving a plurality ofcontrol signals therefrom each having an amplitude corresponding to theamplitude of corresponding ones of the signals to be tested and to thephase displacement of each such signal from the in-phase component ofthe reference signal, a second output circuit coupled to said seconddetector means for deriving a further plurality of control signalstherefrom each having an amplitude corresponding to the amplitude ofcorresponding ones of the signals to be tested and to the phasedisplacement of each such signal from the phase-quadrature component ofthe reference signal, means for impressing said inst-mentioned pluralityof control signals on said rst deection means of said cathode-ray tubeand means for impressing said further plurality of control signals onsaid second deflection means of said cathode-ray tube.

3. Apparatus for indicating the amplitude of a signal to be tested andthe phase of such a signal with respect to a reference signal of likefrequency, said apparatus including in combination, irst and secondelectron discharge devices each including an anode, a cathode and acontrol electrode; a first input circuit for impressing the signal to betested on the respective control electrodes of said first and seconddischarge devices; a second input circuit for impressing an in-phasecomponent of the reference signal on said cathode of said rst device andincluding a phase-quadrature network for impressing a phase-quadraturecomponent of the reference signal on said cathode of said seconddischarge device; means for applying a bias potential between therespective control electrodes and cathodes of said first and seconddevices to cause said devices to operate as half-wave rectiers to thereference signal components applied thereto; a cath= ode-ray tube havinga viewing screen and further having first and second dellection meansfor deflecting a cathoderay beam in the tube across said screen inmutually per'- pendicular directions, a rst output circuit coupled tothe anode of said first device for impressing on said iir'st deectionmeans a first control signal having' an' amplitude corresponding to theamplitude of the signal to be tested and to the phase displacement ofsuch signal from the inphase component of the reference signal; and asecond output circuit coupled to the anode of said second device forimpressing on said second deflection means a second control signalhaving an amplitude corresponding to the amplitude of the signal to betested and to the phase displacement of such signal from thephase-quadrature component of the reference signal.

4. Apparatus for indicating the amplitude of a signal to be tested andthe phase of such a signal with respect to a reference signal of atleast double the amplitude thereof and of like frequency, said apparatusincluding in combination, rst and second pairs of electron dischargedevices, with each of said devices including an anode, a cathode and acontrol electrode; a iirst input circuit for impressing the signal to betested on the respective control electrodes of said rst and second pairsof devices in like phase; a second input circuit for impressing anin-phase component of the reference signal on the respective cathodes ofsaid rst pair of devices in push-pull relation and including aphase-quadrature network for impressing a phasequadrature component ofthe reference signal on said cathodes of said second pair of devices inpush-pull relation; means for applying a negative bias potential to therespective control electrodes of said devices of said iirst and secondpairs to cause said devices to operate as half-wave rectiiiers to thereference signal components applied thereto; a cathode-ray tube having aviewing screen and further having rst and second pairs of deflectionelectrodes for deflecting a cathode-ray beam in the tube across saidscreen in mutually perpendicular directions; a rst pair of outputcircuit respectively coupled to the anodes of said iirst pair of devicesfor impressing on said rst pair of deection electrodes a first controlsignal having an amplitude corresponding to the amplitude of the signalto be tested and to the phase displacement of such signal from thein-phase component of the reference signal; and a second pair of outputcircuits respectively coupled to the anodes of said second pair ofdevices for impressing on said second pair of deiiection electrodes asecond control signal having an amplitude corresponding to the amplitudeof the signal to be tested and to the phase displacement of such signalfrom the phase-quadrature component of the reference signal.

5. Apparatus for indicating the amplitude of a signal to be tested andthe phase of such a signal with respect to a reference signal of atleast double the amplitude thereof and of like frequency, said apparatusincluding in combination, rst and second pairs of electron dischargedevices, with each of said devices including an anode, a cathode and acontrol electrode; a first input circuit for impressing the signal to betested on the respective control electrodes of said tirst and secondpairs of devices in like phase; iirst and second phase-invertinginductive means respectively coupled between the cathodes of said irstand of said second pairs of devices and each having an intermediatepoint thereon connected to a point of reference potential; capacitivemeans coupling the cathode of one of the devices of said iirst pair tothe cathode of one of said devices of said second pair and forming aresonant network with portions of said first and second inductive means;resistor means connecting said last-named cathode to said point ofreference potential; a second input circuit for impressing the referencesignal on said cathode of said one of the devices of said rst 'l Y Y Apair; means for applying a negative bias potential to the respectivecontrol electrodes of said devices of said first and secondpairs tocause said devices to operate `as half- Wave rectiiiers to the referencesignal components applied thereto; a cathode-ray tube having a viewingscreen and further having rst and second pairs of detlection electrodesfor deecting a cathode-ray beam in 'the tube across said screen inmutually perpendicular directions; a first pair of output circuitsrespectively coupled to the anodes of said first pair of devices forimpressing on said first pair of deflection electrodes a rst controlsignal having an amplitude corresponding to the amplitude of the signalto be tested and to the phase displacement of such signal from thereference signal; and a second pair of output circuits respectivelycoupled to Vthe anodes of said second pair of devices for impressing onsaid second pair of deection electrodes a second control signal havingan amplitude corresponding to the amplitude of the signal to ybe testedand to the phase displacement of such signal from a phase-quadraturecomponent of the reference signal.

6. Apparatus for deriving first and second control signals havingrespective amplitudes corresponding to the amplitude of an applied testsignal and to the phase disi placements of such test signal from a likefrequency and at least double amplitude reference signal and from aphase-quadrature component of such reference signal, said apparatusincluding in combination, irst and second pairs of electron dischargedevices, with each of said devices including an anode, a cathode and acontrol electrode; a rst input circuit for impressing the test signal onthe respective control electrodes of said iirst and second pairs ofdevices in like phase; first and second phase-inverting inductive meansrespectively coupled between the cathodes of said first and second pairsof devices and each having an intermediate point thereon connected to apoint of reference potential; capacitive means coupling the cathode ofone of the devices of said first pair to the cathode of one of saiddevices of said second pair; resistor means connecting said last-namedcathode to said point of reference potential; a second input circuit forimpressing the reference signal on said cathode of said one of thedevices of said rst pair; means for applying a negative bias potentialto the respective control electrodes of said devices of said first andsecond pairs to cause said devices to operate as halfwave rectiiiers; arst pair of output circuits respectively coupled to the anodes of saidiirst pair of devices for deriving the iirst control signal therefrom;anda second pair of output circuits respectively coupled to the anodesof said second pair of devices for deriving the second control signaltherefrom.

7. Apparatus for deriving lirst and second control signals havingrespective amplitudes corresponding to the amplitude of an applied testsignal and to the phase displacements of such test signal from a likefrequency and at least double amplitude reference signal and from aphase-quadrature component of such reference signal, said apparatusincluding in combination, first and-second electron discharge deviceseach including an anode, a cathode and a control electrode; a iirstinput circuit for impressing the test signal on the respective'controlelectrodes of said first and second discharge devices; first and secondinductive means respectively coupled between the cathodes of said firstand second devices and a point of reference potentials; capacitive meanscoupling the cathode of said first device to the cathode of said Yseconddevice; variable resistor means connecting said cathode of said seconddevice to said point of reference potential; a second input circuit forimpressing the reference signal on said cathode of said first device;means for applying a negative bias potential to the respective controlelectrodes of saiddevices to cause said devices to operate as 'half-waverectiers; a first output circuit Y 16 t coupled to said anode of saidfirst device for deriving the first control signal therefrom; and asecond output circuit coupled to the anode of said second device forderiving the second control signal therefrom. n

8. Apparatus for deriving first and second control signals havingrespective amplitudes corresponding to the amplitude of an applied testsignal and to the phase displacements of such test signal from a likefrequency reference signal and from a phase-quadrature component of suchreference signal; said apparatus including in combination, lirst andsecond phase detectors for individually producing a signal having anamplitude licorresponding to the phase displacement of a pair of likefrequency signals applied thereto and to the amplitude of at least oneof the applied signals; a first input circuit connected to a point ofreference potential for impressing the test signal on said rst andsecond phase detectors; a second input circuit connected to said pointof reference potential Vfor impressing the reference signal on saidfirst phase detector; capacitive means coupling said second Vinputcircuit to said second phase detector; lirst and second inductive meansrespectivelyconnected from the junctions of said capacitive means withsaid second input circuit and with said second phase detector to saidpoint of reference potential; variable resistor means connected fromsaid junction of said capacitive meansrwith said second detector to saidpoint of reference potential; and

iirst andV second output circuits respectively coupled toV said phasedetectors for deriving'the first and second concomponents, and bursts ofa color reference signal having a selected timing with respect to thesynchronizing components and having the frequency of the Vsub-'carriercomponents and a selected phase relation therewith, said apparatusincluding in combination, .a first channel for selecting the sub-carriercomponents of the color television signal; a second channel forselecting the color television signal and for producing a referencesignal having the phase and frequency of the reference signal bursts inresponse to the color television signal; said second channel inciuding aseparator circuit for separating the synchronizing components from thecolor television signal, a delay line for delaying theseparatedsynchronizing components so that such components occur in timecoincidence with the bursts of color reference signal,

a gated circuit responding to the delayed synchronizing frequency andphase of the color bursts, av tirst phase detector coupled to said firstand second channels kfor producing a first series of control signalshaving individual amplitudes corresponding to the amplitudes of thechroma sub-carrier components and to the phase displacements of suchcomponents from the reference signal, a quadrature phase shiftingnetwork coupled to said second channel, a second phase detector coupledto said first channel and to said quadrature phase shifting network forproducing a second series of control signals having individualamplitudes corresponding to the amplitudes of the chroma sub-carriercomponents and to the phase displacements of such components from aphase-quadrature component of the reference signal; .a cathode-rayreproducing tube including iirst and second deflection means fordeecting a cathode-ray beam in the-tube in mutually perpendiculardirections; and means for VYimpressing said first and second series ofcontrol signals modulating the sub-carrier components translated therebyby a periodic signal to vary the amplitude of such components repeatedlybetween zero and a predetermined maximum.

l1. The apparatus defined in claim 9 in which said second channelincludes an amplitude limiter stage for limiting the amplitude of thereference signal to a constant amplitude at least double the amplitudeof each of the sub-carrier components applied by said first channel tosaid first and second phase detectors.

12. Apparatus for indicating the frequency deviation from centerfrequency of an amplitude-limited frequencymodulated signal, saidapparatus including in combination, a time-delay network, means forimpressing the frequencymodulated signal on said network to cause saidnetwork to transform frequency variations of such signal from the centerfrequency into phase variations; a source of a reference frequencysignal; a first modulator coupled to said source; means for impressingthe frequency-modulated signal on said rst modulator to be heterodynedtherein with the reference frequency signal; a second modulator coupledto said time-delay network and to said first modulator to heterodyne thephase-varying signal from said network with the signal from said firstmodulator to produce an output signal having the frequency of thereference signal and having phase variations with respect theretocorresponding to the frequency variations of the frequency-modulatedsignal; a first phase detector coupled to said reference signal sourceand to said second modulator for producing a first control signal havingamplitude variation scorresponding to the phase variations of the outputsignal from said second modulator with respect to said reference signal;a quadrature phase shifting network coupled to said reference signalsource; a second phase detector coupled to said quadrature phaseshifting network and to said second modulator for producing a secondcontrol signal having amplitude variations corresponding to the phasevariations of the output signal from said second modulator with respectto a phase-quadrature component of said reference signal; a cathode-rayreproducing tube including lirst and second deflection means fordeecting a cathode-ray beam in the tube in mutually perpendiculardirections; and means for impressing said rst and second series ofcontrol signals respectively on said first and second deection means.

13. Apparatus for indicating characteristics of a passive network undertest, said apparatus including in combination, a signal generator forproducing a standard signal of a selected frequency, means for frequencymodulating the standard signal recurrently in equal discrete steps toproduce a repeating series of successive signal components each of adifferent frequency, means for impressing such signal components on anetwork under test, a source of a reference frequency signal, a firstmodulator coupled to said source, means for impressing said repeatingseries of successive signals on said first modulator to cause suchsignals to be heterodyned by the reference frequency signal, a secondmodulator coupled to said first modulator, means for impressing thesignals translated by the network under test on said second modulator tocause such signals to be heterodyned by signals from said rst modulator,whereby said second modulator produces a series of signal componentseach having the frequency of said reference signal and having respectivephase displacements from said reference signal corresponding to thephaseshifting characteristics of the network under test at therespective frequencies of the signals impressed thereon, said series ofsignal components from said second modulator further having respectiveamplitudes corresponding to the attenuation of the network under test atthe respective frequencies of the signal impressed thereon, a firstphase detector coupled to said reference signal source and to saidsecond modulator for producing a series of control signals havingindividual amplitudes corresponding to the amplitudes of said secondmodulator signal components and to the respective phase displacementsthereof from said reference signal, a quadrature phase shifting networkcoupled to said reference signal source, a second phase detector coupledto said quadrature phase shifting network and to said second modulatorfor producing a second series of control signals having individualamplitudes corresponding to the amplitudes of said second modulatorsignal components and to the respective phase displacements thereof froma phase quadrature component of said reference signal, a cathode-rayreproducing tube including first and second deection means fordeflecting a cathode-ray beam in the tube in mutually perpendiculardirections, and means for impressing said rst and second series ofcontrol signals respectively on said rst and second deflection means.

References Cited in the le of this patent UNITED STATES PATENTS

